What is familial adenomatous polyposis?

Familial adenomatous polyposis (FAP) is an inherited disorder
characterized by cancer of the
large intestine (colon) and
rectum. People with the classic type of familial adenomatous polyposis may
begin to develop multiple noncancerous (benign)
growths (polyps) in the colon as early as their
teenage years. Unless the
colon is removed, these polyps will become malignant (cancerous). The average
age at which an individual develops colon cancer in classic familial adenomatous
polyposis is 39 years. Some people have a variant of the disorder, called
attenuated familial adenomatous polyposis, in which
polyp growth is delayed. The
average age of colorectal cancer onset for attenuated familial adenomatous
polyposis is 55 years.

In people with classic familial adenomatous polyposis, the number of polyps
increases with age, and hundreds to thousands of polyps can develop in the
colon. Also of particular significance are noncancerous growths called desmoid
tumors. These fibrous tumors usually occur in the tissue covering the intestines
and may be provoked by surgery to remove the colon. Desmoid tumors tend to recur
after they are surgically removed. In both classic familial adenomatous
polyposis and its attenuated variant, benign and malignant tumors are sometimes
found in other places in the body, including the
duodenum (a section of the
small intestine),
stomach, bones, skin, and other tissues. People who have
colon polyps as well as growths outside the colon are sometimes described as
having Gardner syndrome.

A milder type of familial adenomatous polyposis, called
autosomal recessive
familial adenomatous polyposis, has also been identified. People with the
autosomal recessive type of this disorder have fewer polyps than those with the
classic type. Fewer than 100 polyps typically develop, rather than hundreds or
thousands. The autosomal recessive type of this disorder is caused by mutations
in a different gene than the
classic and attenuated types of familial adenomatous polyposis.